Short answer
Take your normal dose the next day. Don't double up. One missed day won't undo your progress.
If / Then
If you miss one day → just resume the next day at the normal dose.
If you miss several days in a row → still resume at the normal dose; your cellular stores will rebuild over the following 1–2 weeks.
If you stop for 2+ weeks → you're effectively restarting. Expect the first noticeable changes to come back in 7–14 days of consistent use, similar to your original start.
Notes
Consistency is the single biggest factor in results. Missing one stick won't ruin anything — but missing many days in a row resets the cellular stores you've built up.
A practical tip: keep the box somewhere you can't miss it (next to the coffee machine, on the kitchen counter, or in your handbag). The habit follows the location.